From c2fd206e08cd55e7ee0d865affc172eb5af01c16 Mon Sep 17 00:00:00 2001 From: Tony Battersby Date: Thu, 8 Jan 2009 12:58:04 -0500 Subject: [PATCH] [SCSI] sym53c8xx: use a queue depth of 1 for untagged devices sym53c8xx uses a command queue depth of 2 for untagged devices, without good reason. This _mostly_ seems to work ok, but it has caused me some subtle problems. For example, I have an application where one thread sends write commands to a tape drive, and another thread sends log sense polling commands. With a queue depth of 2, the polling commands end up being starved for long periods of time while multiple write commands are serviced (this may also be related to the fact the the sg driver queues commands in LIFO order). This problem is fixed by changing the queue depth to 1 for untagged devices. I have tested this change extensively with many different tape drives, medium changers, and disk drives (disk drives of course use tagged commands and are therefore unaffected by this patch). Signed-off-by: Tony Battersby Signed-off-by: James Bottomley --- drivers/scsi/sym53c8xx_2/sym_glue.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/scsi/sym53c8xx_2/sym_glue.c b/drivers/scsi/sym53c8xx_2/sym_glue.c index a0d5aa6aad7..23e78201588 100644 --- a/drivers/scsi/sym53c8xx_2/sym_glue.c +++ b/drivers/scsi/sym53c8xx_2/sym_glue.c @@ -792,9 +792,9 @@ static int sym53c8xx_slave_configure(struct scsi_device *sdev) /* * Select queue depth from driver setup. - * Donnot use more than configured by user. - * Use at least 2. - * Donnot use more than our maximum. + * Do not use more than configured by user. + * Use at least 1. + * Do not use more than our maximum. */ reqtags = sym_driver_setup.max_tag; if (reqtags > tp->usrtags) @@ -803,7 +803,7 @@ static int sym53c8xx_slave_configure(struct scsi_device *sdev) reqtags = 0; if (reqtags > SYM_CONF_MAX_TAG) reqtags = SYM_CONF_MAX_TAG; - depth_to_use = reqtags ? reqtags : 2; + depth_to_use = reqtags ? reqtags : 1; scsi_adjust_queue_depth(sdev, sdev->tagged_supported ? MSG_SIMPLE_TAG : 0, depth_to_use);